FIG. 1 is a cross-sectional view of a prior art image reader disclosed in Japanese patent publication No.2768866, for example. In the figure, reference numeral 8 denotes a document whose image is being captured, reference numeral 7 denotes a photoelectric conversion unit having a photoelectric transducer 6 aligned in a line, reference numeral 3 denotes a line light source for uniformly applying light to the document 8, reference numeral 2 denotes a plurality of light emitting elements arranged in a line on a substrate for light source, the plurality of light emitting elements consisting of a light emitting diode (LED) chip, for example, reference numeral 14 denotes a transparent plate located under the document 8, the transparent plate consisting of a glass plate, for example, and having a rugged portion used for improving a deflection of the amount of light, reference numeral 5 denotes an optical system (e.g., a rod lens array) located above the photoelectric transducer 6, for converting light and shade information formed on the document 8 into an erect image having the same size as the light and shade information, and reference numeral 4 denotes a housing for housing the photoelectric conversion unit 7, the line light source 3, the transparent plate 14, and the optical system 5, the housing constituting the image reader.
Next, a description will be made as to an operation of the prior art image reader.
The document 8 is carried on the transparent plate 14 and is uniformly irradiated with light emitted out of the light source 3. Light reflected from the document 8 is then formed into an erect image having the same size as the object on the photoelectric transducer unit 6 by the optical system 5 (e.g., a rod lens array) fixedly held in the housing 4, and is then amplified after converted into an electrical signal. Thus a photoelectric-converted output is acquired. The image reader of FIG. 1 can be a facsimile apparatus supporting documents having a size such as A4, in which reading speed is relatively slow and only one direction in which documents are carried is allowed. The prior art image reader assumes that the document whose image is being captured rarely has a bend or broken part.
FIGS. 2(a) to 2(c) are cross-sectional enlarged views each showing a positional relationship between the housing 4 and transparent plate 14 of the prior art image reader. FIG. 2(a) presents a case where the transparent plate 14 is placed at a higher level than the housing 4, FIG. 2(b) presents an ideal case where the transparent plate 14 is placed at the same level as the housing 4, and FIG. 2(c) presents a case where the transparent plate 14 is placed at a lower level than the housing 4. Arrows in FIGS. 2(a) to 2(c) indicate a direction in which the document is carried, and reference numeral 9 denotes a roller for carrying the document 8 while pressing the document 8 towards the transparent plate 14. When there is a difference between the housing 4 and the transparent plate 14 with respect to the direction in which the document is carried, as shown in FIG. 2(a) or 2(c), the head of the document can be jammed and the carrying of the document cannot be carried out well, as shown by reference numerals 8b and 8d. Furthermore, it is actually very difficult to provide an ideal configuration in which the transparent plate 14 is placed at the same level as the housing 4 as shown in FIG. 2(b), and the roller 9 can support only one direction in which the document is carried, the direction being designated by the arrows of FIGS. 2(a) to 2(c). Actually, in the configuration as shown in FIG. 2(a) in which the transparent plate 14 is placed at a higher level than the housing 4, the document is inserted into the image reader such that its head comes into contact with the upper surface of the transparent plate 14, so that the document can be smoothly carried without occurrence of a paper jam of the head of the document.
In recent years, image readers for reading, as the document 8, a check, a vote card for horse racing, or the like have been manufactured based on such a prior art image reader. Such an image reader requires about twice or more speedup as compared with facsimile apparatuses, bidirectional carrying of documents including carrying of documents in a direction in which a wrong inserted document is returned, and a structure that offers stable carrying of documents without occurrence of a paper jam. Image readers for capturing an image of a banknote 80 as the document 8 have recently begun hitting the market, and, when the image of the banknote 80 cannot be captured well because it has a bend or broken part or when a document (including a forged banknote) other than the banknote is inserted, require bidirectional carrying of documents including carrying of documents in a direction in which the inserted banknote 80 is returned.
FIG. 3 is a cross-sectional view showing another prior art image reader. In the figure, reference numerals 10a, 10b, 11a and 11b denote carrying rollers, reference numerals 12a and 12b denote document carrying guides, reference numeral 13 denotes a resin, and reference numeral 15 denotes a document guide.
Because the prior art image reader for capturing the image of the banknote 80 requires at least 5-times or more speedup as compared with facsimile apparatuses, the document guide 15 is disposed on the transparent plate 14, as shown in FIG. 3, instead of the roller 9 used for document carrying, and the image reader is so constructed as to carry the banknote 80 floating apart from the transparent plate 14 along the document carrying guides 12a and 12b arranged before and behind the transparent plate 14 by using the carrying rollers 10a, 10b, 11a and 11b that are arranged before and behind the document guides 12 and 15.
FIG. 4 is a cross-sectional view of another prior art image reader for reading information carried by light passing through a banknote. The image reader of FIG. 4 applies light to the banknote by using a transmission-type light source 17 instead of the light source of FIG. 3, and then reads information carried by the light passing through the banknote. The prior art image reader of FIG. 4 differs from that of FIG. 3 in only the position of the light source, and carries out a reading operation in the same way that the image reader of FIG. 3 does.
Because when there is a difference between the transparent plate 14 and either of the document carrying guides 12a and 12b the banknote 80 that is a document can be blocked or broken by the difference, it is necessary to attach the document carrying guides 12a and 12b to the housing so that they are arranged before and behind the transparent plate 14 by filling gaps between the transparent plate 14 and the document carrying guides 12a and 12b with the resin 13 of normal temperature curing type or the like and with a high degree of accuracy so that there is no difference between the transparent plate 14 and each of the document carrying guides 12a and 12b. It is necessary to take countermeasures to prevent the document carrying guides 12a and 12b from becoming misaligned so that a difference is caused between the transparent plate 14 and either of the document carrying guides 12a and 12b due to a decrease in the adhesive force of the resin 13 according to a heat that occurs in operating environments while the image reader is operating, and to prevent a crack from occurring in the resin 13. It is also necessary to design and assemble the image reader in consideration of the influence of the difference among the thermal expansions of the transparent plate 14, the document carrying guides 12a and 12b, and the housing 4 due to the difference among the temperatures of locations where they are placed, respectively, and it is further necessary to select a material suitable for the resin 13 and to examine a method of curing the material into the resin.
In case where the transparent plate 14 is a glass plate, for example, the transparent plate 14 can have a thickness allowance of about ±0.2 mm. In case where each of the document carrying guides 12a and 12b is a molded object that consists of polycarbonate or the like, each of the document carrying guides 12a and 12b can have a height allowance of about ±0.3 mm. It is therefore necessary to adjust the height of each assembled image reader, to install all the components in the housing in consideration of the parallelism and flatness of each of those components and with difficult manual operations, and to attach the document carrying guides to the housing by filling gaps between the transparent plate and the document carrying guides with the resin 13. Therefore, a problem encountered with such an image reader is that the reliability of the image reader is reduced when a paper jam occurs, and it is necessary to always position a person who performs maintenance when a paper jam occurs near the image reader. Another problem is that when a banknote is carried at a high speed in such an image reader, the image reader cannot always capture the image of the banknote at a high speed because the banknote might go off course due to a wind force.
Old banknotes can have many small cuttings and these small cuttings can become motes and, when the gaps between the transparent plate 14 and the document carrying guides 12a and 12b are not adequately filled with the resin 13 and/or when cracks appear in the resin 13, can enter the housing 14 from the gap between the housing 14 and the transparent plate 14 via the gaps between the transparent plate 14 and the document carrying guides 12a and 12b and/or the cracks in the resin. When motes then adhere to the optical system 5 or the photoelectric transducer 6, a malfunction occurs in the image reader. Therefore, the prior art image reader requires complete overall bonding sealing so that there is no gap between the transparent plate 14 and the housing 4 and no crack appears in the resin 13.
As previously mentioned, a problem with a prior art image reader constructed as mentioned above is that in order to capture an image of such a document as a check or banknote, it is necessary to prevent the document from being jammed in bidirectional carrying of the document, and particularly it is necessary to design and assemble the image reader so that there is no difference between each of the document carrying guides 12a and 12b and the transparent plate 14 when the image reader is used for capturing an image of a banknote.
Another problem is that the reading speed of reading the banknote cannot be raised to solve the problem associated with the carrying of the banknote that the assembly of the image reader is difficult and the reliability of the image reader is low, and it is difficult to completely seal the housing 4 with the transparent plate 14 to prevent small cuttings from entering the housing 4.
The present invention is proposed to solve the above-mentioned problems, and it is therefore an object of the present invention to provide an image reader that can prevent such a document as a check or banknote from being jammed, that can be easily assembled and improve the reliability of carrying, and that enables higher-speed reading.
It is another object of the present invention to provide an image reader that can prevent motes from invading a housing from space between a transparent plate and the housing, and can be easily assembled.